I was watching game when it happened. Weaver falls off the mound when he throws and the batter hit a come backer not directly at his head but enough to cause Weaver to alter his movement putting his arm down to brace himself and move out of the way. When he put his arm down the elbow jammed and then moved in the wrong direction. The ESPN announcers thought he got hit in the head, even though he was grabbing his non-pitching elbow.